Using a rolling ball with physics, the edges of floor segments cause undesirable collisions that make the ball jump up. This is an old problem that used to have a workaround. The workaround was to modify the contact offset settings in the project settings “physics” section. The issue seems to have regressed around version 4.20. There is a UE4 Forum Post that documents the problems that people have had. One thread reply identified the change that is potentially to blame for this undesired behavior.
Setting the contact offset settings no longer improves the physics stability to any reasonable degree. This issue also is seen on BSP meshes, which makes them unusable for such a project.
Here is a 4.22 project that can be used for testing: https://drive.google.com/open?id=1qxyDxr7xzPBzrAxdrR7yzP8aa9puVU5U